The engine won't freeze under normal liveable environmental conditions. As long as you haven't changed the coolant to anything that doesn't contain anti-freeze and follow the engine oil recommendations, you will be perfectly fine. Car engines are built to handle freezing cold environments. For all conditions, cold or not, I always recommend letting the engine idle after first turning it on until the idle revs drop to 1000RPM or lower and until the temperature gauge moves onto the scale and is sitting on or above the cold line. In warmer conditions, this only takes about 30 seconds, but in colder conditions just expect to wait a little longer. After that, just drive it gently till it gets to operating temperature.